The present invention generally relates to the field of disc drives. More specifically, the present invention relates to the field of microactuators for use in disc drives.
Computer systems play a vital and integral role in our modern society and we have come to rely heavily on computer systems in our everyday life. From a simple home computer system to help us with our business, personal and entertainment needs, to a meteorological computer system that models atmospheric patterns to generate a weather forecast, to a traffic control computer system that helps maintain traffic flow, to a telecommunications computer system that routes thousands of telephone calls every minute, computers have a vast and significant impact on our everyday life that is difficult to comprehend.
A critical part of every computer system is a data storage system for storing bits of data or digital information. Electronic memory banks store limited quantities of data that may be useful in small scale computer systems. However, most computer systems utilize vast quantities of data that must be stored by a more practical means. Magnetic disc drives were developed to accommodate the need for a practical and efficient means to store large quantities of information.
Magnetic disc drives typically include one or more flat discs that have a magnetic medium coated on each surface. The magnetic surface on the disc may be modified to write information onto the disc or the magnetic field pattern on the surface may be detected to read information from the disc. In this manner, information may be stored on and retrieved from the disc.
Magnetic disc drives also typically include one or more magnetic heads that perform the reading and writing function. Each magnetic head is positioned over the disc surface at precise locations using an actuator assembly. With this arrangement, the surface of the disc may be divided into discrete tracks each defining a separate radial position on the disc surface. The actuator assembly moves the magnetic head over the desired track to read or write data at that location.
Disc drives have evolved into highly complex electromechanical systems involving many specialized components, rendering a more detailed description of a typical magnetic disc drive necessary for a full understanding of the present invention.
Magnetic disc drives generally utilize a plurality of rigid discs including a magnetizable medium coated on each side or surface of the disc. The discs are rigidly mounted on a spindle motor to form a stack of spaced-apart discs rotatable about the axis of the spindle motor. The discs are mounted such that the axis of the spindle motor (i.e., the axis of rotation) is orthogonal to the disc surface.
Adjacent each disc surface is a magnetic head or slider that xe2x80x9cfliesxe2x80x9d above the disc due to aerodynamic or hydrodynamic lift. Each slider includes an air bearing surface facing the disc surface which creates the lift relative to the rotating disc surface. Each slider also includes one or more transducers that read and/or write to the magnetic medium on the disc surface. Inductive type transducers capable of both reading from and writing to the disc surface may be used alone or in conjunction with MR (magnetoresistive) type transducers capable of reading from the disc.
It is important that the slider remain in close proximity to the disc surface in order to maintain the proper interaction between the transducer(s) on the slider and the magnetic media on the disc surface. As such, it is necessary to compensate for the aerodynamic lift imposed on the slider. This may be accomplished by utilizing a pre-loaded suspension connected to the slider. The proximal end of the suspension is connected to a track accessing arm or primary actuator which is rotatable about an axis orthogonal to the disc surface but is fixed in all other directions. The distal end of the suspension is connected to the slider and exerts a normal force by elastic beam deflection in a direction opposite that of the aerodynamic lift.
The suspension includes a flexible portion referred to as a gimbal and a relatively rigid portion referred to as a load beam. The gimbal portion of the suspension allows the slider to move in the pitch and roll directions and is typically a separate part welded to the load beam portion of the suspension. The gimbal portion may be formed from a thinner material than the load beam to increase its pitch and roll compliance. Alternatively, the gimbal may be formed from partially etched material or from the load beam material itself. The load beam, which transfers the preload force to the slider, is typically made by forming stiffening webs or flanges along the longitudinal edges of the suspension. Alternatively, the rigid load beam portion may be formed by depositing circuit layers on the suspension material.
The pre-loaded force is typically on the order of 0.5 gmf to 4.0 gmf which allows the slider to fly above the disc surface when the disc is rotating at nominal speed, but otherwise causes the slider to be in contact with the disc surface. Because of the potential damage caused by friction between the slider and the rotating disc at sub-nominal speeds, a landing and take-off zone may be provided on the disc surface. The landing and take-off zone has a low coefficient of friction thus reducing the potential for damage to the slider.
The track accessing arm or primary actuator includes a proximally mounted voice coil and a distally mounted extension arm which is connected to the proximal end of the suspension. The voice coil interacts with a magnet to effect controlled rotation of the primary actuator about an axis of rotation (z-axis) orthogonal to the disc surface and disposed between the voice coil and the extension arm. In this manner, the primary actuator moves the slider from track to track across the surface of the disc.
The preload force is typically applied to the slider through a dimple or load button which bears on the back surface of the slider. Alternatively, the preload force is applied through the gimbal structure. The point of preload application is defined as the suspension load point.
In some instances, it is desirable to have a secondary actuator to make minor adjustments in the position of the slider. For example, it may be desirable to correct for off-track errors due to non-concentric tracks or skew angle variance. In addition, it may be desirable to correct for fly height variations due to changes in aerodynamic lift caused by a difference in disc surface speed (inside vs. outside tracks) or a difference in altitude. This may be accomplished by using a microactuator connected between the slider and the suspension for fine positioning of the slider.
Microactuators may also be useful for decreasing the access time of the drive. A microactuator capable of moving the slider to an adjacent track or across a number of tracks would enable seek operations to be performed using the microactuator only, which is faster than using the primary actuator.
The present invention provides a low mass comb-type microactuator positioned between the slider and the transducer. The low mass comb-type microactuator of the present invention allows relatively large travel with voltage-in/displacement out control.
The relatively low mass of the microactuator of the present invention enables the microactuator to operate at a resonant frequency many times higher than the servo frequency with springs that are relatively less stiff than those that would be utilized if the entire slider were actuated. By utilizing relatively flexible springs, the low mass microactuator of the present invention enables relatively large travel with less actuation force. A comb-type microactuator also has the advantage of enabling relatively large displacement as compared to a parallel plate actuator. Voltage-in/displacement-out control of the microactuator has an advantage over voltage-in/acceleration-out control in that it is less complicated because it does not require a position sense signal and feedback circuit to implement.
Specifically, the present invention provides a disc drive data storage system having a disc mounted to a motor, a slider connected to the distal end of an access arm such that the trailing edge of the slider is disposed adjacent the rotating surface of the disc, a comb-type microactuator mounted on the trailing edge of the slider wherein the microactuator includes a stator portion and a rotor portion and a transducer mounted to the rotor portion. The rotor portion of the microactuator and the transducer have a total mass of less than 100 xcexcg, preferably less than 50 xcexcg and ideally less than 10 xcexcg. The microactuator may include a plurality of stator portions and rotor portions connected in parallel. A control circuit may be used to supply signals to the microactuator such that the microactuator has a displacement output of preferably approximately xc2x110 xcexcm or more in response to a voltage input signal of preferably less than about 12 volts.
The stator portion of the microactuator may include a plurality of parallel electrodes mounted on a column. Similarly, the rotor portion may include a plurality of parallel electrodes mounted on another column such that the rotor electrodes are positioned between and parallel to the stator electrodes. The rotor portion may include a transducer mounting surface connected to a spring which is also connected to the slider such that the rotor electrodes move in a substantially parallel path relative to the stator electrodes.
The present invention provides a method of manufacturing a microactuator for use in a disc drive data storage system. The method includes the steps of providing a slider substrate and depositing alternating layers of sacrificial material and stator electrode material onto the substrate. A stator slot and a rotor slot are formed in the alternating layers and a rotor electrode material is deposited into the rotor slot. The sacrificial material is then removed to expose parallel stator electrodes mounted on a column and parallel rotor electrodes mounted on another column such that the rotor electrodes are positioned between and parallel to the stator electrodes.